Modern commercial turkeys are bred for such extreme breast muscle mass that a significant proportion develop deep pectoral myopathy and white striping — painful muscle disorders that affect welfare throughout their lives.
The extreme breast muscle mass developed through selective breeding creates structural problems that cause pain during normal activity. Deep pectoral myopathy occurs because the breast muscle grows faster than its blood supply, causing irreversible tissue death. Turkeys experience this chronic pain for their entire productive lives. The condition is an inherent consequence of the genetic selection for maximum growth, and reducing selection pressure through slower-growing breeds prevents it.